Fuel cells provide electricity from chemical oxidation-reduction reactions and possess significant advantages over other forms of power generation in terms of cleanliness and efficiency. Typically, fuel cells employ hydrogen as the fuel and oxygen as the oxidizing agent. The power generation is proportional to the consumption rate of the reactants.
A significant disadvantage that inhibits the wider use of fuel cells is the lack of a widespread hydrogen infrastructure. Hydrogen has a relatively low volumetric energy density and is more difficult to store and transport than the hydrocarbon fuels currently used in most power generation systems. One way to overcome this difficulty is the use of reformers to convert the hydrocarbons to a hydrogen rich gas stream which can be used as a feed for fuel cells.
Hydrocarbon-based fuels, such as natural gas, LPG, gasoline, and diesel, require conversion processes to be used as fuel sources for most fuel cells. Current art uses multi-step processes combining an initial conversion process with several clean-up processes. The initial process is most often steam reforming (SR), autothermal reforming (ATR), catalytic partial oxidation (CPOX), or non-catalytic partial oxidation (POX). The clean-up processes are usually comprised of a combination of desulfurization, high temperature water-gas shift, low temperature water-gas shift, selective CO oxidation, or selective CO methanation. Alternative processes include hydrogen selective membrane reactors and filters.
Despite the above work, there remains a need for a simple unit for converting a hydrocarbon fuel to a hydrogen rich gas stream for use in conjunction with a fuel cell.
The present invention is generally directed to an apparatus for converting hydrocarbon fuel into a hydrogen rich gas. In one illustrative embodiment of the present invention includes a compact fuel processor for converting a hydrocarbon fuel feed into hydrogen rich gas, in which the fuel processor assembly includes a container having a bottom and substantially vertical sides, a removable top for the container, wherein the removable top includes a manifold, a plurality of connected process units positioned in a spiraling geometry within the container, and a ceramic casting that fills the void space inside the container, wherein the plurality of connected process units forms a channel through the ceramic casting. In such an embodiment, the plurality of connected process units includes an autothermal reforming catalyst bed, a first heat exchanger positioned adjacent to the autothermal reforming catalyst bed, a desulfurization agent bed positioned adjacent to the first heat exchanger, a second heat exchanger positioned adjacent to the desulfurization agent bed, a water gas shift catalyst bed positioned adjacent to the second heat exchanger, a third heat exchanger positioned adjacent to the water gas shift catalyst bed, and a carbon monoxide oxidation catalyst bed positioned adjacent to the third heat exchanger. Optionally, an embodiment of the present invention comprises a second plurality of connected process units positioned within the container, wherein the second plurality of connected process units forms a channel through the ceramic casting, wherein the second plurality of connected process units includes an anode tail gas oxidation catalyst bed, and a pre-heat exchanger positioned adjacent to the anode tail gas oxidation catalyst bed. Such an apparatus utilizes its manifold to provide preheating means for preheating the hydrocarbon before the hydrocarbon fuel contacts the autothermal reforming catalyst bed. In one embodiment of the present invention, each of the first, second, and third heat exchangers has a tube side and a process side, and the preheating means includes introducing the hydrocarbon fuel to the tube side of at least one of the first heat exchanger, the second heat exchanger, or the third heat exchanger. The manifold includes means for introducing the hydrocarbon fuel to the tube side of the third heat exchanger to produce a first preheated feed, means for introducing the first preheated feed to the tube side of the second heat exchanger to produce a second preheated feed, means for introducing the second preheated feed to the tube side of the first heat exchanger to produce a third preheated feed, and means for introducing the third preheated feed to the autothermal reforming catalyst bed. Alternatively, if an anode tail gas oxidizer is included with the processor design, or if a fourth heat exchanger is otherwise included in the design downstream of the preferential oxidation catalyst bed, the manifold also includes means for introducing the third preheated feed to the pre-heat exchanger or the fourth heat exchanger before introducing the preheated feed to the autothermal reforming catalyst bed. It is envisioned that a preferred aspect of the manifold is that the means for routing streams throughout the processor is by use of a piping, tubing, or an equivalent, that flanges or snaps into place in the appropriate locations with the box processor.
Another such illustrative embodiment includes a method for using such a box-shaped compact fuel processor for converting a hydrocarbon fuel feed into hydrogen rich gas. The method includes providing a box-shaped fuel processor comprising an autothermal reforming catalyst bed, a first heat exchanger positioned adjacent to the autothermal reforming catalyst bed, the first heat exchanger having a tube side and a process side, a desulfurization agent bed positioned adjacent to the first heat exchanger, a second heat exchanger positioned adjacent to the desulfurization agent bed, the second heat exchanger having a tube side and a process side, a water gas shift catalyst bed positioned adjacent to the second heat exchanger, a third heat exchanger positioned adjacent to the water gas shift catalyst bed, the third heat exchanger having a tube side and a process side, and a carbon monoxide oxidation catalyst bed positioned adjacent to the third heat exchanger. In this preferred embodiment of the present invention, the box-shaped processor may be used to preheat the hydrocarbon fuel in the tube side of at least one of the first heat exchanger, the second heat exchanger, or the third heat exchanger, then reform the preheated hydrocarbon fuel in the autothermal reforming catalyst bed to produce a first hydrogen product, then remove the sulfur compounds from the first hydrogen product in the desulfurization agent bed to produce a second hydrogen product, then remove carbon monoxide from the second hydrogen product in the water gas shift catalyst bed to produce a third hydrogen product, then introduce an oxygen-containing gas to the third hydrogen product to produce a fourth hydrogen product, and then oxidize the fourth hydrogen product to produce a hydrogen rich gas that is substantially free of carbon monoxide. It is a preferred aspect of this embodiment that the hydrogen rich gas produced is suitable for direct feed to a fuel cell, or for storage in a metal hydride storage system, or contains less than about 50 pmm carbon monoxide, or more preferably less than about 10 ppm carbon monoxide.